1. Technical Field
This invention relates generally to optical relay systems, and more particularly to an optical relay system that includes a substrate guided relay and scanned light source, and which employs a homogenizing input relay device to make copies of an input light beam to provide a more uniform image output.
2. Background Art
Substrate guided relays are devices that transmit light rays from a source to a viewer. Generally, substrate guided relays are optical image transfer devices that include a substrate, which may manufactured from glass or fused silica, and which directs light from a relay input to a relay output. This light can be guided along its path by the optical transfer properties of the substrate. These optical transfer properties can additionally work in tandem with reflective or diffractive devices coupled to the substrate. The surfaces of the substrate can also work to direct the light to its intended destination. In many applications, this end destination is a viewing region that is directed to a projection surface or a user's eye. One application of substrate guided relays is that of a near-to-eye display in which the viewing region projects directly into the pupil of a user.
Substrate guided relays generally include three basic components: an input that collects and receives light from a source, a substrate that transfers the light, and an output that delivers light away from the substrate. In many applications, it is advantageous to keep the various components of the substrate guided relay assembly small, as they are sometimes used as head mounted displays or other compact display systems. This desire to keep size to a minimum creates challenges, however, for the designer. In particular, when a source of light is small, the light often has a smaller spatial extent. It can therefore be challenging for a substrate guided relay designer to create a display having a pupil that is much larger than the extent of the source.
An additional challenge is that it can be advantageous to confine the incident light coming from the source within the substrate guided relay before the beam expands. Such confinement helps to ensure that all of the light projected by a source is captured by the substrate guided relay, rather than being lost to the surrounding environment.
Further, from a fabrication standpoint, it can be challenging to fabricate an input device or substrate of small dimensions with a high degree of precision generally associated with image guiding substrates. Extra thickness or stabilization devices may be required for rigidity, stability, to maintain flatness over a large area when such an input device is heated, cooled, or coated, in the manufacturing process.
The desire to use small light sources and the challenges of manufacturing small input devices can result in an input light beam that is smaller that the input to the substrate guided relay in at least one dimension. Sometimes, this mismatched beam to input ratio can cause dark regions or gaps in the output image where little or no light is present.
There is thus a need for an improved optical relay system capable of enhancing output brightness and uniformity, yet that is compatible with compact, scanned light sources.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.